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Tuesday, February 4, 2014

From a pattern recognition systems standpoint, it appears as the Chinese population's susceptibility to H7N9 infection is bi-modal in distribution. A smaller percentage of the population is readily infected with H7N9, a larger percentage of the population requires a longer dwell time and/or closer exposure to a H7N9 infected environment before becoming infected. These longer dwell times occur during paid national holidays, and infection rates soar.

The system seems to function in the following manner.

(1) There is an avian environmental presence of H7N9

(2) Some individuals are more readily susceptible to catching environmental H7N9

(3) The readily susceptible and H7N9 detectable human population is not ubiquitous enough to sustain chain detectable transmission
(4) During paid holidays increased contaminated interpersonal dwell time increases infectious momentum.
(5) Increased infectious momentum allows the less susceptible to be come infected.
(6) The newly infected less susceptible people increase the opportunity for infection in the more susceptible population and infections spike.
(7) Infection rates in the less susceptible population dampen out as the paid holiday forcing function ends

When we look at a chart of cumulative H7N9 infection dates (see chart below) it is clear that explosive increases in H7N9 detections are tied to paid Chinese National Holidays. It also appears that the infections tend to taper off after the spike, and that they are seasonal in nature.

Of course the question remains, what specifically about human interaction on paid holidays is making the less susceptible all of a sudden vulnerable to infection? We don't know. It could be different immune system responses among the population. It could be that the less susceptible population culturally, normally keeps increased interpersonal distance except during holidays periods. It could be that the infection pool is truly zoonotic in nature and that the transmission chains are also zoonotic.

Based on this conjecture, we expect to see a large spike in H7N9 detections to start as Chinese New Year ends. And we expect that spike to start tapering off in early March. We then expect to see an additional spike tied to International Women's day on March 8th.

If there is no H7N9 spike tied to the Chinese Lunar New Year celebrations, it is reasonable to assume that wet market mitigation actions are responsible, and as a result a prime driver for infection is poultry. However if there is a spike and a follow up spike tied to Women's day, it would tend to indicate that H7N9 is Human to Human and that asymptomatic cases are minimal. Conversely, a Lunar New Year Spike and no Women's day spike might tend to indicate that H7N9 is Human to Human but that it is also wide spread and asymptomatic.